The present invention relates to hydraulic valve mechanisms.
Hydraulic valves are known and widely utilized.
One hydraulic valve is disclosed in the German Offenlegungsschrift No. 2,252,772, in which the functions of the pressure compensation of a pressure compensation valve are performed by a longitudinal valve element, whereas the functions of the throttle means and the direction control of the pressure medium stream to the motor ports are performed by a control valve element. For the functions of a load-maintaining non-return valve, a non-return valve separate from both the above-mentioned control elements is provided. Such a construction has the disadvantage that, for the above-mentioned four functions, three control elements are provided so that the valve is relatively expensive. In addition, the longitudinal axis of the non-return valve extends normal to the longitudinal axis of the control valve element so that the housing of the valve has a relatively great height. Moreover, in the known valve the control edges for the direction control are formed on the control valve element at both sides of the throttle means, which leads to the fact that downstream of the non-return valve for the pressure medium control to and from the motor ports, altogether six working chambers are necessary. This also increases the space consumption for the control valve. By the arrangement of the control edges for the direction control at both sides of the throttle means, the return chamber associated with the control valve element is arranged so far outwardly that a special return chamber must be provided for unloading of the control pressure medium in the region of the throttle means. Thereby, a compact construction of the valve in longitudinal direction of the control valve element is undesirably affected.
Further, a hydraulic valve is disclosed in the German Offenlegungsschrift No. 1,751,934 which is suitable for load-independent control. In this valve, the control edges for the direction control are arranged at one side of the throttle means on the control valve element; however, the throttle means here cooperate with a pressure compensating valve as bypass-flow control unit. This valve has the disadvantage that it does not have a non-return valve which protects the motor ports. In addition, this valve is poorly suitable for a parallel connection of several such valves.